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Friday, July 4, 2014

Sugar addiction: The myth re-visited

I have previously blogged on the myth of sugar addiction[1]
but I return to that subject today on foot of some recent publications. The
first is a chapter in a new book on sugars and health and the section that
attracted my attention was an explanation of the rat studies, which first
suggested that sugar was addictive[2]. The
late Barley G. Hoebel carried out these studies. Rats were given either a
24-hour access to a 10% sugar solution or a 12-hour access to the same
solution. Both groups of rats had access to a standard rat diet, perfectly
balanced for the nutritional needs of this species. Rats live with a “dark” and
“light” cycle of about 12 hours each and it is only during the dark period,
when the lights are switched off, that rats eat. In this particular study, the
rats in the 12-hour arm of the experiment, only received their sugar, some four
hours after the start of the dark cycle. It was well known that if during this
dark eating cycle, a rat is deprived of food for the first few hours, then,
when presented with the food, the rat will gorge itself on the food and will
fully compensate for the period of denial. So when the rats were offered their
10% sugar solution, having spent four hours without access to this highly
palatable food, they did precisely as predicted: they gorged.In fact, during this period of gorging, they
amassed 30% of all their daily calories. Thus, without knowing the subtleties
of rodent dining protocol, one would happily conclude that when rats were given
a sugary solution for a limited period of time, they behaved like alcoholics
let into a free bar after a period of booze restraint. Now what about the rats
that had access to this sugary solution over a 24-hour period? Well, they
consumed exactly the same amount of sugar as their binging, apparently addicted
fellow rats that had just 12-hour access. And just to cap it all, neither group
of rats went on to become obese as they simply reduced their intake of the
standard rat diet. The “addicted” rats showed all the classic neurological
signs of addiction including opioid withdrawal when the sugar is removed or
when they are treated with opioid blocking drugs. However, the relevance of
these studies to humans using this bizarre model is zero.

Which brings me to the second study led by Professor Gary
Frost from Imperial College London[3]. This
study used the Yale Food Addiction Score(YFAS). Most criteria to measure addiction are based on clinical models
but the Yale version is specifically designed to examine the hypothesis of food
(fat and sugar) addiction. The researchers conducted a weight loss intervention
study in 178 severely obese subjects (mean BMI of 36.1 kg/m2) taking
part in a weight loss programme, which used behavioural therapy to reduce body
weight over a 6- month period. They hypotesised that those patients that showed
signs of food addiction according to YFAS would be the least successful in
weight loss and that significantly more of those with food addiction would drop
out. Both hypotheses were shown not to be valid. There was no difference in
weight loss between the two groups and there was no difference in attrition.
This is by far the largest study to examine food addiction in relation to
weight loss.

Consider a study in which alcoholics and social drinkers are
compared for their ability to abstain from alcohol or to minimise their alcohol
intake. The predicted outcome would be that the alcoholics would fare much
worse because their addiction to alcohol is so strong. But that doesn’t happen
with this measure of food addiction. In all, some 15% of subjects were declared
food addictive at baseline which tallies with the general range seen among the
obese population seeking treatment (15-20%). Their “addiction” to food as
measured by the Yale scale is so weak that it is simply over-ridden by a
behavioural therapy programme.

All in all, while the concept of food addiction might seem attractive,
the biology just doesn’t stack up. But, in the area of public health nutrition,
why lets the facts spoil a good media story!

[2]
Are Sugars addictive? Perspectives for practitioners, by Rebecca LW Corwin and
John E Hayes in “Fructose, High fructose corn syrup, sucrose and health, edited
by James M. Rippe and published by Humana Press (2014)

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"Ever seen a fat fox ~ Human obesity explored"

About Me

I graduated from University College Dublin in 1971 with an Masters in Agricultural Chemistry, took a PhD at Sydney University in 1976 and joined the University of Southampton Medical School as a lecturer in human nutrition in 1977. In 1984 I returned to Ireland to take up a post at the Department of Clinical Medicine Trinity College Dublin and was appointed as professor of human nutrition. In 2006 I left Trinity and moved to University College Dublin as Director of the UCD Institute of Food and Health. I am a former President of the Nutrition Society and I've served on several EU and UN committees on nutrition and Health. I have published over 350+ peer reviewed scientific papers in Public Health Nutrition and Molecular Nutrition and am principal investigator on several national and EU projects (www.ucd.ie/jingo; www.food4me.org). My popular books are "Something to chew on ~ challenging controversies in human nutrition" and "Ever seen a fat fox: human obesity explored"